Electrochemical cell

ABSTRACT

The invention describes an electrochemical cell for the electrolysis of an aqueous solution of hydrogen chloride, comprising at least an anode half-cell with an anode, a cathode half-cell with a gas diffusion electrode as cathode and an ion exchange membrane arranged between the anode half-cell and the cathode half-cell, the membrane consisting of at least a perfluorosulfonic acid polymer, wherein the gas diffusion electrode and the ion exchange membrane are adjacent to each other, characterised in that the gas diffusion electrode and the ion exchange membrane, under a pressure of 250 g/cm 2  and at a temperature of 60° C., have a contact area of at least 50%, with respect to the geometric area.

The invention provides an electrochemical cell with a gas diffusionelectrode as cathode and which is particularly suitable for theelectrolysis of an aqueous solution of hydrogen chloride.

A process for the electrolysis of an aqueous solution of hydrogenchloride is disclosed e.g. in U.S. Pat. No. 5,770,035. An anodecompartment with a suitable anode, comprising e.g. a substrate of atitanium/palladium alloy which is coated with a mixed oxide ofruthenium, iridium and titanium, is filled with the aqueous solution ofhydrogen chloride. The chlorine formed at the anode escapes from theanode compartment and is fed to a suitable recovery process. The anodecompartment is separated from the cathode compartment by a commerciallyavailable cation exchange membrane. On the cathode side, a gas diffusionelectrode is mounted on the cation exchange membrane. The gas diffusionelectrode in its turn is mounted on a current distributor. Gas diffusionelectrodes are, for example, oxygen depletion cathodes (ODC). When usingan ODC as a gas diffusion electrode, air, oxygen-enriched air or pureoxygen is normally introduced into the cathode compartment and this isreduced on the ODC.

Commercially available ion exchange membranes have a flat supportstructure of a woven fabric, gauze, braiding or the like made from e.g.polytetrafluoroethylene (PTFE), to one face of which is applied aperfluorosulfonic acid polymer such as e.g. Nafion®, a commercialproduct from DuPont. If this type of ion exchange membrane is used in anelectrolysis cell with a gas diffusion electrode as an oxygen depletioncathode for the electrolysis of an aqueous solution of hydrogenchloride, a relatively high operating voltage, in the region of 1.25 to1.3 V at 5 kA/m², is required.

Therefore the object of the present invention is to provide a membraneelectrolysis cell with a gas diffusion electrode as cathode, inparticular for the electrolysis of an aqueous solution of hydrogenchloride, which has the lowest possible operating voltage.

The invention provides an electrochemical cell for the electrolysis ofan aqueous solution of hydrogen chloride, comprising at least an anodehalf-cell with an anode, a cathode half-cell with a gas diffusionelectrode as cathode and an ion exchange membrane arranged between theanode half-cell and the cathode half-cell, the membrane consisting of atleast a perfluorosulfonic acid polymer, wherein the gas diffusionelectrode and the ion exchange membrane are adjacent to each other,characterised in that the surface of the gas diffusion electrode facingthe ion exchange membrane and the surface of the ion exchange membranefacing the gas diffusion electrode are smooth.

The invention also provides an electrochemical cell for the electrolysisof an aqueous solution of hydrogen chloride, comprising at least ananode half-cell with an anode, a cathode half-cell with a gas diffusionelectrode as cathode and an ion exchange membrane arranged between theanode half-cell and the cathode half-cell, the membrane consisting of atleast a perfluorosulfonic acid polymer, wherein the gas diffusionelectrode and the ion exchange membrane are adjacent to each other,characterised in that the gas diffusion electrode and the ion exchangemembrane, under a pressure of 250 g/cm² and at a temperature of 60° C.,have a contact area of at least 50%, preferably at least 70%, withrespect to the geometric area.

The contact area according to the invention, between the gas diffusionelectrode and the ion exchange membrane under a pressure of 250 g/cm²and at a temperature of 60° C., can be determined, for example, asdescribed in example 5. The trial in accordance with example 5 simulatesthe pressure and temperature conditions in the electrochemical cellaccording to the invention when operating.

The ion exchange membrane consists of at least one layer of aperfluorosulfonic acid polymer such as e.g. Nafion®. Otherperfluorosulfonic acid polymers that can be used for the electrolysiscell according to the invention are described e.g. in EP-A 1 292 634.The ion exchange membrane may also have a support or contain includedmicrofibres for mechanical reinforcement.

The support for the ion exchange membrane is preferably a gauze, wovenfabric, braiding, knitted fabric, non-woven or foam made of anelastically or plastically deformable material, particularly preferablymetal, plastics, carbon and/or glass fibres. PTFE, PVC or PVC-HT areparticularly suitable as plastics materials.

In a preferred embodiment of the ion exchange membrane, the support isembedded in one layer or between at least two layers ofperfluorosulfonic acid polymer. The ion exchange membrane isparticularly preferably built up from at least two layers of theperfluorosulfonic acid, wherein the support for the ion exchangemembrane is embedded between the layers or in one of the two layers ofperfluorosulfonic acid polymer. This can take place, for example, byapplying at least one layer of a perfluorosulfonic acid polymer to eachof the two faces of the support. If the support is embedded in one layeror between at least two layers of the perfluorosulfonic acid polymer,the ion exchange membrane has a smoother surface than an ion exchangemembrane in which only one face of the support has a layer of aperfluorosulfonic acid. A smoother surface for the ion exchange membraneenables better contact with the gas diffusion electrode. The smootherthe surface of the ion exchange membrane, the greater is the area overwhich the ion exchange membrane makes contact with the adjacent gasdiffusion electrode.

The gas diffusion electrode includes an electrically conducting support,preferably made of a woven fabric, braiding, gauze or non-woven made ofcarbon, metal or sintered metal. The metal or sintered metal must beresistant to hydrochloric acid. These include e.g. titanium, hafnium,zirconium, niobium, tantalum and some Hastalloy alloys. The electricallyconducting support is optionally provided with a coating material whichcontains an acetylene black/polytetrafluoroethylene mixture. Thiscoating material can be applied to the electrically conductive supportby spreading with a knife and is then sintered at temperatures of about340° C. This coating material acts as a gas diffusion layer. The gasdiffusion layer can be applied to the entire surface area of theelectrically conductive support. It may also be embedded into all orpart of the open-pored structure of the support, i.e. a woven fabric,braiding, gauze or the like. An electrically conducting support made ofa carbon non-woven which is provided with a gas diffusion layer of anacetylene black/polytetrafluoroethylene mixture is commerciallyobtainable, for example from the SGL Carbon Group.

The gas diffusion electrode also contains a catalyst-containing layer,also called a catalyst layer. The following may be used as a catalystfor the gas diffusion electrode: noble metals e.g. Pt, Rh, Ir, Re, Pd,noble metal alloys, e.g. Pt-Ru, noble metal-containing compounds e.g.noble metal-containing sulfides and oxides, and chevrel phases e.g.Mo₄Ru₂Se₈ or Mo₄Ru₂S₈, wherein these may also contain Pt, Rh, Re, Pd,etc.

A gas diffusion electrode suitable for use in the electrolysis cellaccording to the invention and the production thereof is disclosed ine.g. WO 04/032263 A. Electrical contact with the gas diffusion electrodeis achieved via a current distributor, on which the gas diffusionelectrode lies.

In the electrochemical cell according to the invention, the entire areasof the ion exchange membrane and the gas diffusion electrode which actsas a cathode when the cell is operating are adjacent, wherein the ionexchange membrane and the gas diffusion electrode, under a pressure of250 g/cm² and at a temperature of 60° C., have a contact area of atleast 50%. In general, an electrochemical cell of the type according tothe invention is operated under a pressure of 0.2 to 0.5 kg/m² and at atemperature of 40 to 65° C. The smoothest possible surface is alsodesirable for the gas diffusion electrode because the smoothest possiblesurface improves contact with the ion exchange membrane. In order toproduce the smoothest possible surface, the gas diffusion layer and/orthe catalyst layer can be applied, for example, by means of a sprayprocess, wherein the drops of sprayed dispersion must flow as uniformlyas possible. A suitable spray process is disclosed e.g. in WO 04/032263A. An open-pore, electrically conducting support in which the pores areclosed by the gas diffusion layer is preferably used. The gas diffusionlayer and/or the catalyst layer can also be applied by a machine usingrollers or brushes.

The greatest possible contact area is produced by appropriate choice ofthe gas diffusion electrode and ion exchange membrane. Both of thesemust have the smoothest possible surface and at the same time the bestpossible microdeformability, i.e. good deformability in the micronrange.

In a special embodiment of the electrolysis cell according to theinvention, the catalyst layer for the gas diffusion electrode is appliedto the ion exchange membrane. The catalyst layer can be applied to theion exchange membrane, for example, by spraying on or by means of a filmcasting process disclosed in the prior art. In this way the ion exchangemembrane and the catalyst layer form a membrane electrode unit (MEU). Inthis case, the electrically conducting support with the gas diffusionlayer is adjacent to the catalyst layer. Here, the contact areaaccording to the invention of at least 50%, preferably at least 70%,with respect to the geometric area, under a pressure of 250 g/cm² and ata temperature of 60° C., is between the gas diffusion layer and thecatalyst layer of the MEU.

The electrolysis cell according to the invention has a 100 to 300 mVlower operating voltage during the electrolysis of an aqueous solutionof hydrogen chloride (hydrochloric acid).

In a preferred embodiment, the ion exchange membrane is built up from atleast two layers, wherein the layers have different equivalent weights.The equivalent weight, in the context of the invention, is understood tobe the amount of perfluorosulfonic acid polymer which is required toneutralise 1 litre of 1 N caustic soda solution. The equivalent weightis thus a measure of the concentration of the ion-exchanging sulfonicacid groups. The equivalent weight of the ion exchange membrane ispreferably 600 to 2500, in particular 900 to 2000.

If the ion exchange membrane is built up from several layers withdifferent equivalent weights, then, in principle, the layers may bearranged in any way at all with respect to each other. However, an ionexchange membrane is preferred in which the layer of ion exchangemembrane which faces the gas diffusion electrode, i.e. is adjacent tothe gas diffusion electrode, has a higher equivalent weight than theother layers. If, for example, the ion exchange membrane is built upfrom two layers, then the equivalent weight of the layer facing theanode is 600 to 1100 and the equivalent weight of the layer facing thegas diffusion electrode is 1400 to 2500. If more than two layers arepresent, then the equivalent weight can increase from the layer facingthe anode in the direction towards the layer facing the gas diffusionelectrode. However, it is also possible to arrange layers with higherand lower equivalent weights in an alternating manner, wherein the layeradjacent to the gas diffusion electrode has the highest equivalentweight.

Chlorine transport through the ion exchange membrane can be reduced bychoosing the equivalent weight and by choosing layers with differentequivalent weights. The smallest possible migration of chlorine throughthe ion exchange membrane is desirable. In the ideal case, the migrationof chlorine should be completely suppressed because chlorine is reducedto chloride in the catalyst layer of the gas diffusion electrode andforms dilute hydrochloric acid with the water of reaction formed in thecathode half-cell. On the one hand this cannot be used again andtherefore has to be disposed of. On the other hand contact of dilutehydrochloric acid with the gas diffusion electrode leads to overvoltagesand possibly also to corrosive damage to the catalyst present in the gasdiffusion electrode.

Furthermore, the transport of water from the anode half-cell through theion exchange membrane into the cathode half-cell should be reduced toabout one third in the electrochemical cell according to the invention.This is also of advantage because less dilute hydrochloric acid, whichhas to be disposed of, is formed in the cathode half-cell in this way.Another advantage of the small extent of water transport is that thereis less risk of forming a film of water on the surface of the gasdiffusion electrode. This in turn improves oxygen transport through thegas diffusion electrode.

The anode in the electrochemical cell according to the inventionconsists of gauze, woven fabric, knitted fabric, braiding, or the like,preferably of an expanded metal of e.g. Pd-stabilised titanium which isprovided e.g. with a coating of a Ru-Ti mixed oxide. A suitable anode isdisclosed in e.g. WO 03/056065 A.

EXAMPLES Example 1

Gas diffusion electrodes like those disclosed in U.S. Pat. No. 6,402,930and U.S. Pat. No. 6,149,782 were tested with a proton-conducting ionexchange membrane of the perfluorosulfonic acid type supplied byFumatech, with an equivalent weight of 950, in a laboratory test using alaboratory cell which had an electrochemically active area of 100 cm².

The ion exchange membrane had an internally located support fabric ofglass fibres as a support, i.e. the support was embedded in theperfluorosulfonic acid polymer. The ion exchange membrane used isdescribed in EP-A 129 26 34.

The gas diffusion electrode had the following structure: an electricallyconductive layer of carbon fabric was provided with a gas diffusionlayer comprising an acetylene black/polytetrafluoroethylene mixture. Acatalyst layer comprising a catalyst/polytetrafluoroethylene mixture wasapplied to this support provided with the gas diffusion layer. Therhodium sulfide catalyst was adsorbed on carbon black (Vulcan® XC72).Since the gas diffusion electrode was operated in direct contact with anion exchange membrane, it was also provided with a layer of Nafion®, aproton-conducting ionomer, in order to produce better linkage to the ionexchange membrane. The surface of the oxygen depletion cathode wasapproximately smooth, apart from typical shrinkage cracks due to themanufacturing process. The oxygen depletion cathodes used are describedin U.S. Pat. No. 6,149,782. The current distributor in the oxygendepletion cathode was an expanded titanium metal with a Ti/Ru mixedoxide coating.

A commercially available anode of expanded titanium/palladium metal witha titanium/ruthenium mixed oxide coating was used as the anode. Underthe operating conditions of 5 kA/m², 60° C., 14% technical gradehydrochloric acid and a distance of 3 mm between the anode and the ionexchange membrane pressed onto the cathode under a hydrostatic pressureof 200 mbar, the test cell exhibited an operating voltage of 1.16 V whenoperated continuously for 16-days.

Example 2 (Comparison Example)

The oxygen depletion cathodes described in example 1 were tested with aproton-conducting ion exchange membrane of the Nafion® 324 type fromDuPont under the conditions described in example 1, in severalcomparison trials.

The oxygen depletion cathodes were from the same production batch as theoxygen depletion cathodes used in example 1.

One face only of the ion exchange membrane was coated with theperfluorosulfonic acid polymer, not both faces, wherein the support wasmounted on the oxygen depletion cathode in the form of a supportingfabric. This meant that adequate areal contact between the oxygendepletion cathode and the perfluorosulfonic acid polymer on the ionexchange membrane was not possible. The structure of the support fabricincreased the roughness of the surface. Operating voltages of 1.31 to1.33 were found during the comparison trials.

Example 3

Tests with oxygen depletion cathodes with different surface roughnesseswere performed in the arrangement described in example 1 and under theoperating conditions defined in example 1.

In a first test, an ion exchange membrane from Fumatech was tested withan oxygen depletion cathode which consisted of a carbon non-woven,filled with a gas diffusion layer (as described in example 1) andsprayed with a catalyst layer comprising 30% rhodium sulfide on carbonblack of the Vulcan® XC72 type and Nafion® ionomer solution. The oxygendepletion cathode had a surface roughness of about 140 μm; see example5. This electrode exhibited a stable operating voltage of 1.28 V.

In a second test, this oxygen depletion cathode was tested with an ionexchange membrane of the Nafion® 324 type from DuPont. A voltage of 1.32V was found. Thus, this showed that both the smoothness of the membraneand also the smoothness of the oxygen depletion cathode are critical fora large area of contact between the ion exchange membrane and the gasdiffusion electrode.

Example 4

Chlorine diffusion through different ion exchange membranes was tested.This is expressed, in combination with the water transport index underthe operating conditions, as different hydrochloric acid concentrationsin the catholyte. The following membranes were tested under open-circuitconditions in the zero current state:

-   -   Nafion® 117: monolayered with an equivalent weight of 1100; no        supporting fabric    -   Nafion® 324: two layers with equivalent weights of 1100 and 1500        respectively; with an externally mounted supporting fabric        facing the oxygen depletion cathode, i.e. the support was not        embedded in the perfluorosulfonic acid polymer.    -   Ion exchange membrane from Fumatech, monolayered with an        equivalent weight of 950 and an internally located supporting        fabric, i.e. the support was embedded in the perfluorosulfonic        acid polymer (called Fumatech membrane 950 in the following).

The following behaviour with regard to chlorine diffusion was observedin a 7-hour test:

Nafion® 117: 3511 mg of chlorine

Nafion® 324: 503 mg of chlorine

Fumatech membrane 950: 1144 mg of chlorine

In addition, it was found that, with comparable operation of the threetypes of membrane, the Nafion® membranes had a water transport index ofabout 1 (i.e. 1 mol of H₂O per mol of protons through the membrane)under the conditions mentioned in example 1, whereas the Fumatechmembrane had a water transport index of only 0.37, i.e. about one third.

It was shown that the monolayered Nafion® 117 membrane and the Fumatechmembrane 950 had chlorine diffusions which differed by a factor of morethan 3, wherein the advantage lay with the Fumatech membrane, despitethe low equivalent weight.

On the other hand, the fact that Nafion® 324 had two layers, incombination with a higher equivalent weight for the layer on the cathodeface, resulted in a lowering of the chlorine transport to about 1/7 ascompared with Nafion® 117 and to about one half as compared with theFumatech membrane 950.

In view of the low chlorine diffusion, an ion exchange membrane with acombination of two or more layers with different equivalent weights ispreferred, wherein the equivalent weight increases in the directiontowards the oxygen depletion cathode. A considerable reduction inchlorine diffusion, optionally down to approximately zero, can beproduced in this way. The very low water transport index of the Fumatechmembrane, about ⅓ as compared with the Nafion® membranes, enablesoperation of the oxygen depletion cathode in the moist, i.e. not in thewet, state. Operation in the wet state is known for all Nafion®membranes.

Example 5

The contact area between gas diffusion electrodes (GDE) and ion exchangemembranes, while simulating the conditions prevailing in an electrolysiscell, was determined with the aid of the following laboratory trial.

One face of a strip of ion exchange membrane of about 3×7 cm² was soakedwith 30 μl of a fluorescent solution. The fluorescent solution was madeup in a glycerine/water mixture. For this purpose, fluorescein powderwas dissolved in water and glycerine was added thereto. Thewater:glycerine ratio was 1:1 (80 mg of fluorescein, 4.7 g of water, 4.7g of glycerine).

The ion exchange membrane soaked on one face was stretched over aneoprene fine foam cushion so that the soaked face was adjacent to thefine foam cushion. This face, turned towards the fine foam cushion, isalso called the lower face in the following. The neoprene foam cushionsubstrate had a size of 2.2×2.2 cm².

The upper face of the ion exchange membrane was also wetted with 30 μlof the fluorescent solution. Then the surface was covered with a glassplate and a weight of about 200 g was applied thereto. This distributedthe fluorescent solution on the upper and lower faces on the ionexchange membrane uniformly over the two faces.

The ion exchange membrane soaked in this way and applied to a fine foamcushion was stored in a desiccator for 3 hours at 100% humidity and roomtemperature. The membrane was then thoroughly soaked throughout. Afterstorage in the desiccator, any residual liquid film was removed from thetwo faces of the ion exchange membrane.

The gas diffusion electrode with an area of 2.2×2.2 cm² was laid on theion exchange membrane (the face turned towards the ion exchange membraneis also called the upper face in the following). The current distributorwas mounted on the rear face of the gas diffusion electrode, i.e. theface turned away from the ion exchange membrane. The appropriate weightto provide an applied pressure of 250 g/cm² was placed thereon. Thisentire structure was stored for 19 h in a dessicator in a drying cabinetat 100% humidity and 60° C.

After storage, the gas diffusion electrode was taken out and fixed on amicroscope slide for microscopic assessment.

Assessment using a confocal laser scanning microscope Leica TCS NT:

A general image of the GDE surface was obtained with back-scattering andfluorescence contrast. The image area was 6.250×6.250 mm². Thephotomultiplier gain of the back-scattering channel was set at 322 voltsfor full laser power (about 22 mW, laser output). The photomultipliervoltage for the fluorescence channel was 1000 V. The images were takenin mode 488/>590 nm. Using this setting, the slide was illuminated withthe wavelength 488 nm from the Ar⁺ laser. The back-scattering image wasrecorded at the same wavelength. The image in the fluorescence channelwas drawn up from the fluorescent light from the sample surface which isat wavelengths longer than 590 nm.

The images for assessment were taken with the objective×10/0.3 air. Theimage area was then 1.0×1.0 mm². For statistical reasons, 8 image areaswere taken. Since the surface had obvious topographic structures, seriesof sectional views were taken. With the gas diffusion electrode inaccordance with example 1 (carbon tissue electrode) the difference inheight to be overcome was about 70 μm, with the carbon non-wovenelectrode it was about 140 μm. The images were also recorded in mode488/>590 nm. In the case of the carbon tissue electrode a series ofsectional views of 72.9 μm with 63 individual slices was taken eachtime. The gain at the back-scattering channel was 231 volts, the gain atthe fluorescence channel was 672 volts.

In the case of the carbon non-woven electrode a series of sectionalviews of 143 μm with 127 individual slices was taken each time. The gainat the back-scattering channel was 266 volts, the gain at thefluorescence channel was 672 volts.

A topography image was drawn up from the set of image data from theback-scattering channel. A projection image was produced from the set ofimage data from the fluorescence channel. On this projection image, onlythe palest point from the series of sectional views running in the zdirection was shown for each xy coordinate. This image was used forfurther image analysis assessment of the surface coating.

A histogram was plotted in a fixed image frame with an enclosed area of261632 pixels. The frequencies of each intensity (0-255) occurring wasdetermined from this histogram (see table 1).

Table 1, given below, gives the contact area determined in this way as a%-age, as well as the mean square deviation over 8 measurements fordifferent combinations of ion exchange membranes and gas diffusionelectrodes. The following were used as gas diffusion electrodes: carbontissue electrode in accordance with example 1 (also called type A in thefollowing), carbon non-woven electrode in accordance with example 3,wherein the carbon non-woven had been filled with a gas diffusion layerand sprayed with a rhodium sulfide catalyst layer as well as a Nafion®ionomer solution (also called type B in the following) as well as carbonnon-woven electrodes which were coated with an open-pore gas diffusionlayer and had been sprayed with a rhodium sulfide catalyst layer and aNafion® ionomer solution (also called type C in the following). Anopen-pore coating is understood here to be a coating which does notclose the pores in the carbon non-woven or the like. An open-porecoating can be produced, for example, by soaking the support, e.g. thecarbon non-woven, whereas in the case of a closed-pore, i.e. filled,coating, the gas diffusion layer is applied, for example, to thesupport, which fills the pores in the support.

The following commercially available membranes were used as ion exchangemembranes: ion exchange membranes of the perfluorosulfonic acid typefrom Fumatech with an internal, i.e. embedded, support in accordancewith example 1 (called Fumatech 950), ion exchange membranes of theperfluorosulfonic acid type from DuPont with an external, i.e. notembedded, support in accordance with example 2 (called Nafion® 324) aswell as ion exchange membranes of the perfluorosulfonic acid type fromDuPont without a support (called Nafion® 105).

The voltage was measured at 5 kA/m² and 60° C.

The results in table 1 show that a large contact area between ionexchange membrane and gas diffusion electrode is associated with a lowercell voltage than is a small contact area. TABLE 1 Ion exchange Gasdiffusion Contact area Mean square Voltage membrane electrode [%]deviation [V] Fumatech 950 type A 76.5 2.8 1.16 Nafion ® 105 type A 74.42.3 1.17 Fumatech 950 type B 18.0 3.0 1.28 Nafion ® 324 type B 8.3 1.51.32 Fumatech 950 type C 75.3 4.1 1.22 Nafion ® 324 type C 6.5 1.6 1.31

1-10. (canceled)
 11. An electrochemical cell for electrolysis of anaqueous solution of hydrogen chloride comprising: a) an anode half-cellcomprising an anode, b) a cathode half-cell comprising a gas diffusionelectrode as the cathode, and c) an ion exchange resin comprising aperfluorosulfonic acid polymer which is positioned between a) and b) inwhich a surface of the gas diffusion electrode and a surface of theperfluorosulfonic acid polymer are adjacent to each other and thoseadjacent surfaces are smooth.
 12. An electrochemical cell forelectrolysis of an aqueous solution of hydrogen chloride comprising: a)an anode half-cell comprising an anode, b) a cathode half-cellcomprising a gas diffusion electrode as the cathode, and c) an ionexchange resin comprising a perfluorosulfonic acid polymer which ispositioned between a) and b) in which (i) a surface of the gas diffusionelectrode and a surface of the perfluorosulfonic acid polymer areadjacent to each other and (ii) under a pressure of 250 g/cm² and atemperature of 60° C., the gas diffusion electrode and the ion exchangemembrane have a contact area of at least 50% of their geometric area.13. The electrochemical cell of claim 12 in which the contact area ofthe gas diffusion electrode and ion exchange membrane is at least 70%.14. The electrochemical cell of claim 11 in which the ion exchangemembrane comprises one layer of a perfluorosulfonic acid polymer inwhich a support is embedded.
 15. The electrochemical cell of claim 12 inwhich the ion exchange membrane comprises one layer of aperfluorosulfonic acid polymer in which a support is embedded.
 16. Theelectrochemical cell of claim 13 in which the ion exchange membranecomprises one layer of a perfluorosulfonic acid polymer in which asupport is embedded.
 17. The electrochemical cell of claim 11 in whichthe ion exchange membrane comprises at least two layers ofperfluorosulfonic acid polymer and a support member is embedded betweenthe two layers or in at least one of the layers.
 18. The electrochemicalcell of claim 12 in which the ion exchange membrane comprises at leasttwo layers of perfluorosulfonic acid polymer and a support member isembedded between the two layers or in at least one of the layers. 19.The electrochemical cell of claim 13 in which the ion exchange membranecomprises at least two layers of perfluorosulfonic acid polymer and asupport member is embedded between the two layers or in at least one ofthe layers.
 20. The electrochemical cell of claim 17 in which the twolayers of perfluorosulfonic acid polymer have different equivalentweights.
 21. The electrochemical cell of claim 18 in which the twolayers of perfluorosulfonic acid polymer have different equivalentweights.
 22. The electrochemical cell of claim 19 in which the twolayers of perfluorosulfonic acid polymer have different equivalentweights.
 23. The electrochemical cell of claim 11 in which theperfluorosulfonic acid polymer has an equivalent weight of from 600 to2500.
 24. The electrochemical cell of claim 12 in which theperfluorosulfonic acid polymer has an equivalent weight of from 600 to2500.
 25. The electrochemical cell of claim 13 in which theperfluorosulfonic acid polymer has an equivalent weight of from 600 to2500.
 26. The electrochemical cell of claim 11 in which theperfluorosulfonic acid polymer has an equivalent weight of from 900 to2000.
 27. The electrochemical cell of claim 12 in which theperfluorosulfonic acid polymer has an equivalent weight of from 900 to2000.
 28. The electrochemical cell of claim 17 in which theperfluorosulfonic acid layer with one of its surfaces facing the gasdiffusion electrode has a higher equivalent weight than any otherperfluorosulfonic acid layer.
 29. The electrochemical cell of claim 18in which the perfluorosulfonic acid layer with one of its surfacesfacing the gas diffusion electrode has a higher equivalent weight thanany other perfluorosulfonic acid layer.
 30. The electrochemical cell ofclaim 11 in which a catalyst layer for the gas diffusion electrode isapplied to the ion exchange membrane.
 31. The electrochemical cell ofclaim 12 in which a catalyst layer for the gas diffusion electrode isapplied to the ion exchange membrane.
 32. The electrochemical cell ofclaim 11 in which the ion exchange membrane has a support structurecomprising a gauze, woven fabric, braided fabric, knit fabric, non-wovenmaterial, plastic foam or elastically deformable material.
 33. Theelectrochemical cell of claim 12 in which the ion exchange membrane hasa support structure comprising a gauze, woven fabric, braided fabric,knit fabric, non-woven material, plastic foam or elastically deformablematerial.
 34. The electrochemical cell of claim 11 in which the ionexchange membrane has a support structure comprising metal, plastic,carbon fibers or glass fibers.
 35. The electrochemical cell of claim 11in which the ion exchange membrane has a support structure comprisingmetal, plastic, carbon fibers or glass fibers.